% https://github.com/cmhughes/latexindent.pl/issues/24
\begin{lem}
    \label{1.19:lem1}
    \[ \left\{ 
    \begin{matrix}
        p \in \al\\
        q \notin \al 
    \end{matrix}
    \right\}\implies p < q.\]
\end{lem}
